Defects or voids are caused in bones or teeth by traffic accidents and ablation of osteoncus in the fields of surgery and orthopaedic surgery, and by periodontoclasia, alveoloclasia, odontectomy and cutting-off of dental caries in the field of dental surgery. Various materials including one's own bone, polymers, metals, ceramics etc. have been used to fill such defects and voids, as well as for the dental prosthesis. Among them, one's own bone is excellent since it has high bone forming capacity and causes little rejection. However, as one's own bone must be taken from the one's normal bone tissue, the operation causes great pain and in many cases not enough tissue can be secured. Thus, recently, hydroxyapatite has been replacing the use of one's own bone tissue. Hydroxyapatite can be obtained by synthesized or by sintered animal bones, and removing organic components, and it is known to have excellent biocompatibility. However, when hydroxyapatite in powder or granular form is used as a filling material, such problems as the tendency for it to run-off with blood or body fluids, or transuded as a foreign body even after suturing have been pointed out.
For cementing and fitting a prosthesis in the hard tissue bone-cement has been used. As the bone-cement, so called medical polymers based on PMMA (polymethyl methacrylate) have been used in most cases, however, these materials show insufficient biocompatibility and have such problems as the pain in the affected part caused by the reaction heat generated during the hardening reaction, or the harmfulness of the non-reached monomer to the living body.
Meanwhile, a dental cement material has been used not only as a coalescent for prosthesis, but also as a filling material or a lining material, and various dental cement materials have been developed as restortion materials in the field of dental surgery. Among them, glass ionomer cement, as shown in British Patent Number 1,316,129 made of glass powder produced by melting alumina and silica at a high temperature using a flux such as fluoride, and a hardening liquid made of a copolymer of acrylic acid and an unsaturated carboxylic acid, exhibits great crushing resistance after hardening, relatively good adhesion to tooth, and minimum harmfulness to dental pulp. However, it has a problem of insufficient biocompatibility.
In this context, a new dental cement made of such inorganic components that constitute the hard tissue have recently been drawing attention, and cements based on calcium phosphate or apatite type crystalline powder have been under development as well. The main components of these materials are bone analogues and have excellent biocompatibility, but the reactivity of the crystalline powder with an organic hardening liquid is very bad, since the components that react with the hardening liquid are very limited. Compositions for filling bones and teeth comprising .alpha.-tricalcium phosphate and a liquid component, have been disclosed in U.S. Pat. No. 4,677,140, however, since the crushing resistance of the cement is very low, they cannot be employed for practical use.
Those dental cement materials developed so far have different merits and demerits respectively, and need to be chosen according to the particular purpose, however, the commonly required characteristics of a dental cement material include sufficient hardening characteristics and biocompatibility, and a material satisfying both of them has been desired.
In addition, no materials having both biocompatibility and X-ray opacity have been found for the medical or dental uses. It is needless to say that biocompatibility is very important for a biomaterial, but, in the case of an artificial material to be implanted in a body in some way, it is also important to know the condition of the artificial material when it is implanted, or to follow its change with time correctly. Thus, X-ray opacity also becomes an important property. In order to render X-ray opacity, a metal oxide or a metal salt of such a metal as strontium, barium or lanthanum have been typically blended as X-ray opacity material with the base material. However, those X-ray opacity components do not have biocompatibility, and have high solubility in a living body, or have problems in causing harmful effects including allergies. In view of the above-described problems, a material whose X-ray opacity component per se has biocompatibility and which can remain stable in a living body has also been strongly desired.